Transport signatures of Bogoliubov Fermi surfaces in normal metal/time-reversal symmetry broken $d$-wave superconductor junctions

TL;DR

This paper theoretically investigates how Bogoliubov Fermi surfaces in $d$-wave superconductors influence charge transport signatures, revealing unique conductance features linked to topologically protected BFSs and their interplay with Andreev bound states.

Contribution

It introduces a theoretical framework to identify transport signatures of BFSs in $d$-wave superconductor junctions, emphasizing the role of crystal orientation and interface states.

Findings

Zero-bias conductance enhancement as a signature of BFSs at $ ext{α}=0$

Anomalous zero-bias conductance behavior due to interplay of ABS and BFSs for $ ext{α} eq0$

Behavior persists at finite temperatures and is explained via Fano factor analysis.

Abstract

In recent times, Bogoliubov Fermi surfaces (BFSs) in superconductors (SCs) have drawn significant attention due to a substantial population of Bogoliubov quasiparticles (BQPs) together with Cooper pairs (CPs) in them. The BQPs as zero energy excitations give rise to captivating and intricate charge dynamics within the BFSs. In this theoretical study, we propose to reveal the unique signatures of the topologically protected BFSs in bulk $d$-wave SCs using normal metal/time-reversal symmetry (TRS) broken $d$-wave SC hybrid setup, in terms of the differential conductance and Fano factor (FF). Orientation of crystal $a$ axis with respect to junction normal, quantified by the parameter $\alpha$, is crucial for transport properties in these hybrid devices. For $\alpha=0$, an enhancement in zero-bias conductance (ZBC) can be identified as a key signature of BFSs. However, for $\alpha\ne0$, this feature does not replicate due to the presence of the localized Andreev bound state (ABS) at the interface. The interplay of ABS and BFSs gives rise to an anomalous behavior in ZBC compared to the $\alpha=0$ case. This behavior remains qualitatively similar even at finite temperatures. Finally, we explain this anomalous behavior by analyzing the effective charge of the carriers in terms of the FF. The simplicity of our setup based on $d$-wave SC makes our proposal persuasive.